In general, a vertical field effect transistor differs from a conventional field effect transistor by the fact that its conductive channel extends generally perpendicularly to the substrate, thereby offering the particular advantage of making it possible to improve the integration of such a transistor in integrated circuits.
In the vertical field effect transistors that are manufactured at present, the control gate is formed either by implanting ions (JFETs), or else by depositing metal (permeable base transistors) in the bottoms of trenches etched in the semiconductor.
From the manufacturing point of view, it is less difficult to perform an ion implanting operation to form the control gate of a vertical field effect transistor than it is to perform a metallization operation. With respect to performance, in particular switching speed, a metallized control gate gives better results than a gate formed by implanting ions because of the lower resistivity of the metallized gate. In contrast, a gate formed by implanting ions makes it possible to obtain good rectifying characteristics.
The object of the invention is to design a novel vertical field effect transistor capable of benefitting from the advantages of a transistor where the control gate is formed by implanting ions and of a transistor where the gate is metallized, without having the drawbacks thereof and while also obtaining advantages specific to this novel transistor.